Method for starting an electric motor in a hydraulically operated working machine

ABSTRACT

The invention relates to a method for starting at least one asynchronous electric motor of a large hydraulic excavator having a service weight &gt;100 t and having an electrohydraulic drive, in that the particular electric motor is transferred from an idle position to an operating position by using a three-stage motor starting process, wherein the volumetric flow rate of at least one hydraulic pump operatively connected to the electric motor is set to the delivery rate V=0 during all starting stages of the electric motor and the delivery rate V of the hydraulic pump is controlled to a value &gt;0 only after the last starting stage of the electric motor by activating an actuator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to international patent application number PCT/DE2011/001531, having a filing date of Jul. 29, 2011, which claims the benefit of priority to German patent application number DE102010033346.8, having a filing date of Aug. 4, 2010, the complete disclosures of which are hereby incorporated by reference for all purposes.

TECHNICAL FIELD

The invention relates to a method for starting at least one asynchronous electric motor of a large hydraulic excavator having a service weight >100 t.

BACKGROUND

DE 86 02 103 describes a hydraulic excavator having a chassis which is provided with wheels or caterpillar tracks and forms an undercarriage, having a superstructure which is rotatably connected to said chassis and serves to be rotatable about a vertical axis and has at least one electric motor which is arranged in the undercarriage or superstructure and drives at least one hydraulic pump which feeds the hydraulic drives with pressure medium, and having a cable which is connected to the undercarriage.

DE 198 31 121 A1 discloses a starting circuit with a starting transformer for a three-phase short-circuit rotor motor and having contactors for setting a plurality of starting stages, wherein switch-over elements composed of a contactor and a reactor and in the form of voltage stages are connected between two starting stages in each case.

DE 198 04 043 A1 discloses a starting circuit with a starting transformer for a three-phase short-circuit rotor motor, wherein the starting circuit has contactors for setting a first starting stage for starting the motor, wherein at least one further starting stage can be set with the contactors, wherein in addition a stage can be set for the normal operation of the motor with the contactors, and wherein an electronic control device is provided for controlling the switching over into the various stages in accordance with a determined motor current.

WO 2008/095525 A1 describes an electrohydraulic control arrangement for actuating a hydraulic consumer, comprising a fluid pump which can be adjusted in terms of its expulsion volume, an electric drive which has a variable rotational speed and can be coupled to said fluid pump in order to drive it, and a pressure measuring device for measuring a fluid pressure. A main control circuit is provided whose actuator element is a rotary speed actuator element of the electric drive and by means of which fluid pressure and/or a downstream manipulated variable can be measured and adjusted, wherein an expulsion volume actuator element of the fluid pump can be actuated by means of a secondary adjustment chain as a function of the measured fluid pressure.

Large hydraulic excavators such as are used, inter alia, in mining operations and which are equipped with electric-motor-operated drives require a brief flow of current, corresponding to 4 to 6 times the rated motor current, from the power supply company to start the respective electric motor. In order to obtain this high energy requirement without bringing about a power system collapse at the operator's end, contemporary large hydraulic excavators are operated with a two-stage circuit for the starting process, wherein in the first stage the electric motor is operated with a reduced voltage within a defined time and subsequently with the full power system voltage after the second stage has been activated.

A disadvantage of this switching operation is that during the switching-over process from the first stage into second stage brief current peaks occur which can cause the voltage in an existing power system to collapse.

SUMMARY

The objective of the subject matter of the invention is to make available a method for starting at least one electric motor of a hydraulically operated large hydraulic excavator which no longer has the specified disadvantages, with the result that approximately load-free starting of the at least one electric motor can be brought about.

This objective is achieved in that the volume flow of at least one hydraulic pump which is operatively connected to the electric motor is set to the delivery quantity V=0 during all the starting stages of the electric motor, and the delivery quantity V of the hydraulic pump is not adjusted to a value >0 until after the last starting stage of the electric motor, by activating an actuator element.

According to a further idea of the invention, the respective asynchronous electric motor is activated using the Korndorfer starting method which is known per se.

The method according to the invention is advantageously intended to be used in the field of an electrohydraulically driven large hydraulic excavator having a service weight >100 t.

The subject matter of the invention involves the advantage that approximately load-free starting of the respective electric motor can be ensured by means of the three-stage starting of the at least one electric motor in combination with the reduction of the hydraulic delivery volume flow to the delivery quantity V=0 of at least one hydraulic pump. The disadvantages referred to above no longer occur with the use of the subject matter according to the invention.

It is particularly advantageous that the delivery quantity of the hydraulic pump has the value 0 in each of the three starting phases of the electric motor. This applies even if the electric motor is already running at the full rotational speed. Pressure is only applied to the hydraulic pump, advantageously embodied as an axial piston pump, via a pilot control valve as a result of activation of an actuator element, e.g. manual deflection of a hand lever, and only then is the delivery quantity increased to a value >0, toward the maximum delivery quantity.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the invention is illustrated in the drawing on the basis of an exemplary embodiment and described as follows. In the drawing:

FIGS. 1 to 5 show basic outlines of a diagram relating to the activation of a hydraulic drive with an electric motor.

Identical parts are provided with identical reference symbols for the sake of better clarity.

DETAILED DESCRIPTION

FIG. 1 shows the basic position (inoperative position) in which the voltage is present at an opened switch 1 via the line 8. The delivery quantity V of the hydraulic pump 13 has the value 0.

FIG. 2 shows the first switching stage of the starting process of an electric motor 6 of a hydraulic excavator (not illustrated further) having a service weight >100 t. The switching elements 1 and 3 are closed. The electric current flows through the closed switching element 1 and via electrical lines 8 and 9 to a transformer 2. The switching element 3 is closed at the star point 5 of the transformer 2. This results in a partial electrical current being output to the electric motor 6 at the tapping point 7 of the transformer 2 via electrical lines 10 and 12. The delivery quantity V of the hydraulic pump 13 which is embodied as an axial piston pump in this example also has the value 0.

FIG. 3 shows the second switching stage of the starting process. In this second starting stage, the switching element 3 is opened at the star point 5 of the transformer 2. The upper part of the transformer 2 then acts as a reactor. The delivery quantity V of the hydraulic pump 13 also remains at the value 0 in this switching stage.

FIG. 4 shows the third switching stage of the starting process of the electric motor 6. After the expiry of a predefined time, the switching element 4 is closed by a control unit 16 (not described in more detail). The rated current is taken up directly by the electric motor 6 via the closed switches 1 and 4. In this switching position, the rated voltage of the electric motor is already applied thereto. In this last switching stage, the delivery quantity V of the hydraulic pump 13 also remains at the value 0.

FIG. 5 then shows the connection of the hydraulic pump 13, embodied as an axial piston pump, into the circuit. The hand lever 22 of the actuator element 21 is deflected and therefore closes the switch 18. A command sequence is triggered in the electronic control unit 16 (not described further) as a result of activation of the switch 18, which command sequence electronically actuates a 15 via the output 17 of the control unit 16 in such a way that a hydraulic flow, which is delivered by an auxiliary pump 14, is applied, via the proportional valve 15, to the hydraulic pump 13 which is embodied as an adjustment pump. The adjustment pump 13 is adjusted toward the direction of the delivery quantity V=max through the interaction of the actuator element 21, composed of the hand lever 22 and the switch 18 operatively connected thereto, with the control unit 16 and the hydraulic circuit 14, 15, 19, 20. 

1. A method for starting at least one asynchronous electric motor of a large hydraulic excavator having a service weight >100 t with an electrohydraulic drive, comprising: transferring the respective electric motor from an inoperative position into an operative position by using a three-stage motor starting process; wherein the volume flow of at least one hydraulic pump which is operatively connected to the electric motor is set to the delivery quantity V=0 during all the starting stages of the electric motor, and the delivery quantity V of the hydraulic pump is not adjusted to a value >0 until after a last starting stage of the electric motor, by activating an actuator element.
 2. The method as claimed in claim 1, wherein the respective electric motor is activated using the Korndorfer starting method.
 3. The method as claimed in claim 1, wherein, in a first switching stage a control unit closes electrical switching elements, wherein the delivery quantity V of the hydraulic pump remains at the value
 0. 4. The method as claimed in claim 3, wherein, in a second switching stage the switching element is opened at the star point of a transformer, wherein the delivery quantity V of the hydraulic pump remains at the value
 0. 5. The method as claimed in claim 4, wherein, a third switching stage a pilot control valve remains closed and the delivery quantity V of the hydraulic pump remains at the value
 0. 6. The method as claimed in claim 1, wherein after the last starting stage of the electric motor, an actuator element which is embodied as a hand lever is deflected manually, and the delivery quantity V is adjusted between a value >0 and a maximum delivery quantity V max. as a function of the degree of deflection of the hand lever.
 7. The method as claimed in claim 1, wherein an axial piston pump is used as the hydraulic pump.
 8. A large hydraulic excavator, comprising: at least one asynchronous electric motor configured to be started by a three-stage motor starting process during which a volume of flow of at least one hydraulic pump which is operatively connected to the electric motor is set to the delivery quantity V=0 during all starting stages of the electric motor, and the delivery quantity V of the hydraulic pump is not adjusted to a value >0 until after a last starting stage of the electric motor, by activating an actuator element.
 9. The large hydraulic excavator as claimed in claim 8 wherein, in a first switching stage a control unit closes electrical switching elements and the delivery quantity V of the hydraulic pump remains at the value
 0. 10. The large hydraulic excavator as claimed in claim 9, wherein, in a second switching stage the switching element is opened at the star point of a transformer and the delivery quantity V of the hydraulic pump remains at the value
 0. 11. The large hydraulic excavator as claimed in claim 10, wherein, in a third switching stage a pilot control valve remains closed and the delivery quantity V of the hydraulic pump remains at the value
 0. 12. The large hydraulic excavator as claimed in claim 11, wherein after the last starting stage of the electric motor, an actuator element which is embodied as a hand lever is deflected manually, and the delivery quantity V is adjusted between a value >0 and a maximum delivery quantity V max. as a function of the degree of deflection of the hand lever.
 13. The large hydraulic excavator as claimed in claim 8, wherein an axial piston pump is used as the hydraulic pump. 